Thermal SiO and H${}^{13}$CO${}^{+}$ Line Observations of the Dense Molecular Cloud G0.11$-$0.11 in the Galactic Center region

Abstract

We obtained the first view in H${}^{13}$CO${}^{+}$ $J=1-0$ and a high resolution map in thermal SiO lines of G0.11$-$0.11, which is a molecular cloud situated between the Galactic Center radio arc and Sgr A. From a comparison with previous line observations, we found that the H${}^{13}$CO${}^{+}$ $J=1-0$ line is optically thin, whereas the thermal SiO lines are optically thick. The line intensity in H${}^{13}$CO${}^{+}$ $J=1-0$ shows that the cloud has a large column density, up to $N({\mathrm{H}}_2)=(6-7)\times 10^{23}\mathrm{c}{\mathrm{m}}^{-2}$, which corresponds to about 640--740 mag in $A_{\mathrm{V}}$ or 10--12 mag in $A_{25\mu \mathrm{m}}$. The estimated column density is the largest known of any even in the Galactic center region. We conclude from the intensity ratio of SiO $J=1-0$ to CS $J=1-0$ that emitting gas is highly inhomogeneous for SiO abundance on a scale smaller than the beam width $\sim$35\arcsec.

11 pages, 4 figure pages, accepted for publication in ApJ